The dimensions you mentioned are exactly the dimensions of my Red Bellied's cage, and I'm thinking about getting one larger for her, because she's so hyper! Like Natacha said, bar spacing is a really critical factor. For red Bellieds, it should be 3/4" at the very max, preferably 1/2". I'd say just see how busy your little guy is and how much out of cage time he gets, then go from there!